Abstract

We report the demonstration of a terahertz quantum-cascade laser that operates up to 164 K in pulsed mode and 117 K in continuous-wave mode at approximately 3.0 THz. The active region was based on a resonant-phonon depopulation scheme and a metal-metal waveguide was used for modal confinement. Copper to copper thermocompression wafer bonding was used to fabricate the waveguide, which displayed improved thermal properties compared to a previous indium-gold bonding method.

Figures (4)

(a) Calculated conduction band schematic, with the four-well module outlined in a dotted box. Beginning with the left injection barrier, the layer thicknesses in Å are 49/79/25/66/41/156/33/90, and the 156 Å well is doped at 1.9×1016 cm-3, which yields a sheet density of 3.0×1010 cm-2 per module. (b) Scanning electron micrograph of the cleaved facet of a 23-µm-wide ridge waveguide. (c) Modal intensity for fundamental mode calculated with finite-element solver.

Optical power versus current measured from a 48-µm-wide, 0.99-mm-long ridge using 200-ns pulses repeated at 10 kHz. The lower inset shows an expanded version of the high temperature L-I curves. The upper inset displays the threshold current density versus temperature.

Continuous-wave characteristics for a 23-µm-wide, 1.22-mm-long ridge at various heat sink temperatures, where the optical power is measured from a single facet. The lower panel displays the V-I and dV/dI-I characteristics at several temperatures. The upper inset shows typical spectra at several temperatures, and the lower inset displays the relative size of the threshold discontinuity in the differential resistance versus temperature.

(a) Two-dimensional heat flow model calculated with a nonlinear finite-element solver. The 800-µm-wide, 170-µm-thick n+ GaAs substrate extends beyond the margins of the figure. The lower boundary is set to 117 K, and the active region is uniformly driven by a power source of 1.1×107 W/cm3, which corresponds lasing conditions at Tsink=117 K cw operation.